1. Field of the Invention
The present invention relates to a washing machine having a hybrid sensor and a control method thereof wherein the hybrid sensor can sense a laundry weight, a feed water weight and dynamic unbalance of a washing tub.
2. Description of the Prior Art
In a washing machine, water currents are generated by a pulsator rotated by a motor to exert impact on the laundry, thereby washing the laundry. Washing, rinsing, draining and dehydrating steps are previously programmed in a microcomputer provided for controlling the washing process of a washing machine. When either one of such programs is selected by the user, the laundry is automatically washed according to the selected program.
That is, the washing machine senses the weight of the laundry placed in the washing tub, sets an appropriate water level corresponding to the sensed laundry weight, supplies water to the set water level, and performs washing and rinsing steps. After the rinsing step, the washing machine performs the dehydrating step by which the washing process is completed. In order to achieve a fully automatic washing process, a sensor for detecting the laundry weight, a sensor for detecting a feed water weight and a sensor for detecting dynamic unbalance of the washing tub are all needed for a conventional washing machine.
FIG. 1 is a cross-sectional view of a conventional washing machine having the aforementioned three sensors.
As shown in FIG. 1, the conventional washing machine includes: a laundry weight sensor 10 for sensing a laundry weight; a water level sensor 20 for determining if water is supplied to a water level predetermined in response to the sensed laundry weight; and an unbalance sensor 30 for sensing dynamic unbalance of a washing tub 3.
The laundry weight sensor 10 includes: a permanent magnet 11 being fixedly mounted to a pulley 6 of a washing motor 5, and being rotated with the washing motor 5; and a coil 12 for generating a variable electrical signal as it approaches the permanent magnet 11. The sensor 10 senses the weight of the laundry by utilizing the fact that when the moter 5 is further rotated by inertial force after stopping, the number of its rotation is varied upon the weight of the laundry. That is, if the user puts the laundry in the washing tub and turns on a power switch, a control unit (not shown) of a washing machine rotates the washing motor 5 during a given time and then stops the washing motor 5. As a result, the washing motor 5 is further rotated by inertial force.
The laundry weight is obtained by counting the number of signal pulses generated from the coil 12 magnetized by the permanent magnet 11 during the inertial rotation. If the laundry weight is determined, the control unit sets an appropriate water level according to the laundry weight.
The water level sensor 20 includes: an air trap 21 provided to a lower portion of the water tub 2, the inner air of which is compressed in response to a water level; and a mechanical pressure sensing member 22 for generating variable frequencies ranging from 22 kHz to 26 KHz according to the air pressure of the air trap 21. In operation of the water level sensor 20, as the level of water in the water tub 2 rises by supplying water into the washing machine, the air in the air trap 21 is compressed and exerts a pressure to the mechnical pressure sensing member 22, thereby generating variable frequencies of the range of 26 kHz-22 kHz.
Such a variable frequency is input to the control unit, and the control unit recognizes the present water level. If the present water level reaches to a predetermined water level corresponding to the laundry weight sensed by the sensor 10, the water supply is stopped, and the washing, rinsing and dehydrating steps are sequentially performed.
The unbalance sensor 30 includes: a lever 31 which is apart from an upper end of the water tub 2 for sensing an abnormal motion of the water tub 2 due to an unbalance rotation of the washing tub 3; and a switch 32 which is connected to one end of the lever 31 and generates an on-signal according to the movement of the lever 31 or the opening of the washing machine's door.
If the water tub 2 is swung by unbalance rotation of the washing tub 3 and then operates the lever 31, the switch 32 generates on-signals and the control unit recognizes the unbalance rotation of the washing tub 3 by analyzing the on-signals.
In the meantime, reference numerals 1, 4 and 8 are a main body, a pulsator and suspension bars, respectively.
However, since such a conventional washing machine should be provided with the various sensors aforementioned, namely, a laundry weight sensor, a water level sensor and an unbalance sensor, the production cost of a washing machine is increased, and its inner structure becomes complicated, thereby causing more fabrication steps.
In addition, since the laundry weight sensor 10 senses the laundry weight by utilizing inertial force, it is difficult to measure an accurate laundry weight when the laundries are unevenly distributed in the washing tub 3. If the laundry weight is inaccurately sensed, an optimum feed water weight corresponding to the accurate laundry weight can not be set, thereby lowering the cleaning effect of the laundry.